1. Field of the Invention
The present invention relates to a spindle protective structure in a spindle-through coolant feeder.
2. Description of Related Art
As a spindle structure for use in a high-speed rotating machine tool such as a drilling machine and a tapping machine or a machining center, there is known a spindle-through coolant feeder for feeding machining fluid to a tip of a tool attached to a spindle through a hole formed axially in the spindle for cooling cutting edges of the tool and removing chips.
Such spindle-through coolant feeders are known as a spindle structure in which a spindle is driven by a spindle motor through a transmission device such as a gear train or a belt and coolant is supplied from the through hole of the spindle, a spindle structure in which the spindle is directly coupled with a rotor shaft of the spindle motor and coolant is supplied through the through hole of the spindle and a through hole formed axially in the rotor shaft, and a spindle structure in which the spindle and the spindle motor are combined to form a built-in motor.
In recent spindle-through coolant feeders, coolant of high pressure is generally used for increasing the efficiency of discharging chips and cooling cutting edges of the tool to improve a finished state of a workpiece. Therefore, if an excessive overflow of coolant is caused at a rotary joint, there is a risk that a large amount of coolant may leak outside in a moment. In the case of the above first mentioned spindle structure, coolant may reach peripheries of the spindle, and in the case of the secondly and thirdly mentioned spindle structures, coolant may directly invade the spindle motor or the built-in motor, to possibly cause serious problems such as rust, abnormal rotation or electrical failure. Further, if coolant is not properly supplied to the tip of the tool, cutting edges of the tool or a workpiece may be damaged.
Thus, it is necessary to prevent the coolant from invading the spindle and the spindle motor. However, if a general oil seal which is an effective measure for preventing fluid leakage is used, a temperature of a lip of the oil seal increases because of heat generated by friction between a surface of the shaft rotating at high-speed and the lip to exceed an allowable temperature range of the general oil seal. Thus, the general oil seal is not used for the above-mentioned spindle structure and only a seal member of non-contact type such as a fringer or labyrinth type has been adopted.
FIG. 6 is a cross-sectional view of a seal stricture in a spindle structure for a machine tool or a machining center with a spindle extending in the horizontal direction, as proposed in U.S. Pat. No. 5,967,716.
A rotary joint support housing 12 is fixed to an end face of a spindle motor 8 by bolts 16 led though holes formed at a flange 14. The spindle motor 8 and the rotary joint support housing 12 are aligned by engagement of an inner circumferential face of the flange 14 and an outer circumferential face of a spigot 17 provided on the end face of the induction motor 8.
The interior of the rotary joint support housing 12 is divided into three chambers 12a, 12b and 12c by partition walls 18 and 19 in an axial direction of a rotor shaft 9. A drain pipe 6 and an auxiliary drain pipe 27 are connected to the housing 12 at the lower portion thereof, to communicate with the chamber 12a and the chamber 12b, respectively. A fringer 28 is fixed to the rotor shaft 9 in the chamber 12c to rotate with the rotator shaft 9 to splash dust and fluid radially outward by centrifugal force of the rotation.
A rotary joint 3 is composed of a nipple-like rotary member 22 which is fixed on a distal end of the rotor shaft 9 and rotates with the rotary shaft 9, and a stationary member 23 fixed to the housing 12. A through hole 10 formed axially in the rotor shaft 9 has a tapered pipe thread at its end, and the rotary member 22 is screwed into the through hole 10 to be finely fixed to the rotor shaft 9. The stationary member 23 is fixed to the housing 12 such that a socket portion 23a thereof projects into the chamber 12a to be positioned in confronting relation to the rotary member 22. A pipe 4 for supplying coolant is connected to the stationary member 23.
Coolant supplied from a pipe 4 is lead through an inner conduit in the stationary member 23 to the socket portion 23a and transits from the socket portion 23a to a through hole in the rotary member 22 to be introduced into the through hole 10 of the rotor shaft 9. Coolant leaked out in the transition from the socket portion 23a to the rotary side member 22 is discharged by the drain pipe 6 from the chamber 12a. 
A circular groove 24 is formed on an inner surface of the through hole of the partition wall 18 in sliding contact with the circumferential surface of the rotary member 22. Compressed air or the like is supplied to the chamber 12a from an air purge pipe 26 through a thin hole 25 formed in the partition wall 18 in the radial direction and the circular groove 24, to raise the pressure in the chamber 12a so that the coolant overflowed in the chamber 12a is reliably discharged through the drain pipe 6 to the outside.
Further, coolant in the chamber 12b is discharged through the auxiliary drain pipe 27, and coolant in the chamber 12c is splashed radially outward by the fringer 28 and discharged from cutouts 29 formed at a lower circumference of the housing 12. Further, a flow rate sensor is provided in a flow passage of the drain pipe 6 so that an alarm is issued when a flow rate of coolant flowing in the pipe 6 exceeds a set value.
As described, for preventing the coolant overflowed from the rotary joint from invading the spindle and the spindle motor, the non-contact type seal structure such as the fringer type or a labyrinth-type is adopted. As described, this is because a general oil seal is not adoptable for such a seal structure because of the high-speed rotation of the spindle.
However, if an excessive overflow is caused in the transition from the stationary member 23 to the rotary member 22 of the rotary joint 3, there is a risk that discharge by the non-contact seal structure using the fringer 28 may not be enough to prevent the leaked coolant from invading the spindle and the spindle motor.
An object of the present invention is to provide a spindle protective structure capable of protecting a spindle and a spindle motor from being invaded by leaked coolant in a case where a large amount of coolant overflowed.
A spindle protective structure in a spindle-through coolant feeder of the present invention comprises: a jointing device for feeding coolant into a through hole formed axially in a spindle or a shaft connected to the spindle; a housing for supporting the jointing device; a drain pipe for discharging coolant overflowed in the housing from the jointing device; and a seal member having elasticity for sealing a circumferential surface of a portion of the spindle or the shaft projected into the housing.
The above spindle protective structure is applicable to a spindle structure in which the spindle and a rotor shaft of the spindle motor are connected, to a spindle structure in which the spindle is directly coupled with a rotor shaft of the spindle motor and coolant is fed through the through hole formed axially in the spindle and the through hole formed axially in the shaft, and further to a spindle structure in which the spindle and the spindle motor are combined together to form a built-in motor.
The housing has one or more chambers and the drain pipe and/or the seal member are provided for at least one of the chambers.
The interior of the housing may be divided into a plurality chambers by at lest one partition wall and the seal member may be arranged on the partition wall between the chambers.
A non-contacting seal device such as a fringer or labyrinth may be provided in the housing in addition to the seal member.
The sealing of the circumference of the spindle or the shaft by the seal member is enhanced by pressure of the coolant overflowed in the housing. The seal member may have an elastic lip to be pressed towards the circumferential surface of the spindle or the shaft by the pressure of the coolant overflowed in the housing.
The seal member may have a slight or substantially no interference in fitting the spindle of the shaft to reduce heat generated by friction in contact with the circumferential surface of the spindle or the shaft.